Electromagnetic audio amplifiers



June 7, 1955 F. G. LOGAN I 2,710,313

ELECTROMAGNETIC AUDIO AMPLIFIERS 5 Sheets-Sheet l' Fild Oct. 12; 1948 I46- saunas INVENTOR. 6 7mm 61 104,4

A Arm/mm June 7, 1955 F. g. LOGAN 2,710,313

ELECTROMAGNETIC AUDIO AMPLIFIERS Filed 001.. 12-, 1948 5 Sheets-Sheet 2INVENTOR. flaw/r 6'. Loaa/v June 7, 1955 F. 5. LOGAN 2,710,313

ELECTROMAGNETIC AUDIO AMPLIFIERS 5 Sheets-Sheet 5 Filed Oct. 12, 1948 45array/v5 June 7, 1955 LOGAN 2,710,313

ELECTROMAGNETIC AUDIO AMPLIFIERS Filed Oct. 12, 1948 5 Sheets-Sheet 4 QI I Q 0' O I "f o' o INVENTOR. Fir/mar 6. [0619 June 7, 1955 F. e. LOGAN2,710,313

ELECTROMAGNETIC AUDIO AMPLIFIERS Filed Oct. 12, 1948 5 Sheets-Sheet 5Jgr/K INVENTOR.

h ATTORNEY United S s Paten "mis 2,710,313 ELECTROMAGNETIC AUDIOAMPLIFIERS Frank G. Logan, Kirkwood, Mo., assignor to VickersIncorporated, Detroit, Mic-in, a corporation of Michigan Applicationilctober 12, 1948, Serial No. 54,169 3 Claims. (Cl. 179 -171) Thisinvention relates to electromagnetic audio amplifiers applicable to awide variety of uses and to signal amplifiers and controls within theaudio range. it particularly relates to what may be termed a push-pulltype of control and to various relationships thereof and cornbinationstherewith.

One object is to provide audio amplifiers which avoid the use of vacuumtubes with their likelihood of failure and their necessity of more orless frequent replacement. Another object is to produce audio amplifierswhich will be dependable in long continued use and substantially freefrom deterioration and the necessity of replacement of parts. A furtherobject is to produce apparatus of a simple character which may bereadily manufactured and assembled. Another object is to produceapparatus adapted for low as Well as high output units. Other objects,advantages and applications will be understood from the followingdescription and accompanying drawings which illustrate preferredembodiments ofthe invention.

Fig. 1 is a diagram showing a single stage of amplification of thepush-pull type; Figs. la and 1b showmodifled forms or" couplings to theoutput circuit; Fig. 2 is a diagram of a single stage of this type witha modified form of controlling current; Fig. 3 is adiagrarn showing twostages of amplification wherein the first stage is of the single endedform and the second stage is of the push-pull type; Fig. 3a shows amodified form of coupling between the two stages; Fig. 4 is a diagramsimilar to Fig. 3 showing a different form of control applied to thesecond stage; Fig. 5 is a diagram showing two stages of amplificationeach of the push-pull type; Fig. 6 is similar to Fig. 5 except as toderivation of the control current applied to the second stage; Fig. 7 isan explanatory chart; Fig. 8 shows one form of combined core andwindings, as distinguished from the use of sep-- arate or individualcores; Fig. 9 is another explanatory chart; Fig. 10 is a diagram showingone amplification stage of the push-pull type whereinnon-self-saturating reactors are used; Fig. 11 is a diagram similar toFig. 10 except as to the character of the control current; and Fig. 12is a diagram showing two stages of amplification wherein the first stageutilizes non-self-saturating reactors and the second stage utilizesself-saturating reactors.

The accompanying disclosures are based upon the use of amplifyingreactors which may be of the self-saturat-' ing type or of thenon-self-saturating type. The signal or audio input to the amplifyingapparatus has, of course, a variable frequency within the range that iscapable of being heard; and in order to obtain amplified reproduction offair quality the input power must have a frequency higher than that ofthe highest audio frequency or of the si nal frequency that is to beamplified. In order to obtain good quality of reproduction the inputpower frequency should be several times that of the highest audiofrequency which it is desired to be amplified. Where the input signal oraudio input had a range of from to 3,000 cycles per second, good resultshave been obtained by using a power input having a frequency of 10,800cycles per second. Where the input signal or audio input had a range offrom 30 to 10,000 cycles per second; good results have been obtained byusing a power supply having a frequency of 30,000 cycles per second.

Figure 7 of the accompanying drawings is a chart showing thecharacteristics of a self-saturated reactor Where the controllingmagnetoinotive force is plotted asthe abscissas and the controlledoutput current is plotted 2,710,3l3 Patented June 7;, 1955 as theordinates. In the present invention the steep part of the curve or rangefrom B to C is utilized and the nearer this approaches a straight linethe better is the quality of reproduction.

When the controlling magnetomotive force is at 0 on the chart and themagnetization of the reactor is adjusted to yield a controlled outputcurrent having a value at or near the middle of the steep portion of theline, as at A, the controlling action may be indicated as Class A. Inthis case when the controlling magnetoinotive force is in a positivedirection, that is to the right of the zero in Fig. 7, the output of thecontrolled current will be increased from A toward C; and when thecontrolling magnetomotive force is negative, that is to the left of thezero, the controlled output current will be decreased from A towards B.In the present invention the controlling magnetomotive force is that dueto the variable controlling current from the input signal or audiosource; and the controlled output current is that due to the poweroutput of higher frequency as modulated by the controlling magnetomotiveforce. When the controlling current and controlling magnetomotive forcehas a variable positive and negative direction, it is advantageous tooperate the reactor on the basis of Class A. Referring to Fig. 7, itshould be noted that the change in the output current from A to C andfrom A to B is very pronounced as compared with the required change inthe controlling magnetomotive force for obtaining these limits. Alsowhen the controlling magnetomotive force is increased in a negativedirection beyond where the condition B is obtained, no appreciablechange in output current is obtained and it only begins to rise slightlyunder a very considerable increased magnetomotive force in a negative oropposing direction.

Another mode of control differs from Class A and may be designated asClass B. Referring to Fig. 7, consider the control magnetomotive forceto have a zero value indicated on the figure at 0 and that the outputcurrent at such zero value is of an amount to have a value correspondingto the location B on the line. This is obtainable by adjustment of themagnetization of the reactor core to have such a value when thecontrolling magnetomotive force is zero as at 0. Under such conditionsany change in value of the controlling magnetomotive force in a positivedirection gives a wide and very pronounced range of control from B to Con the line. In this case the controlling current for causing change ofthe controlling mag netoniotive force is effective in responsive resultsonly as regards variations in value thereof in one direction only. Whenthe reactor is controlled in this manner by changes of value of themagnetomotive force in one direction only it is designated as Class Bcontrol. Obviously the most effective response is then obtained when therange of control is effectively utilized over the range from B to C.

Fig. 1 shows an embodiment operable as Class A of the push-pull typewith one stage of amplification. Four separate reactors of the ring typeare shown for simplicity, although they may be of any suitable form andthe two upper; reactors may be combined in one unit of suitable designand the two lower reactors may similarly be combined. The signal oraudio source is indicated as a microphone 1 in circuit with a battery 2supplying current to the primary 3 of a transformer. The power source ofalternating current indicated as A. C. source has a frequency higherthan that of the highest frequency of the signal source and preferablyseveral times higher; and may be of any type for securing the desiredfrequency at approximately constant voltage. This source suppliescurrent to a transformer having a primary winding 4 and two secondarywindings 5 and 5a for securing an output of the desired constant voltagevalue.

The reactor cores 6, 6a, 6b and 6c are respectively provided with loadcurrent windings '7, 7a, 7b and 7c,

the upper windings 7 and 7a being supplied with current from thesecondary winding and the lower windings 7b and 70 being supplied withcurrent from the secondary winding 5a. The windings 7 and 7a areconnected in parallel with each other from one terminal of the winding 5and in series with the winding 7 is a half-Wave valve 8; and in serieswith the winding 7a is a half-wave valve 8a. These valves are preferablyof the dry plate type but may be tubes, crystals or of other forms. Theoutput sides of the valves are connected together but the valves areconnected in reversed relation with reference to each other with theresult that the output therefrom is alternating. Thus the load windings7 and 7a alternately carry intermittent direct pulsating currents. Thesewindings supply current to a full wave rectifier 9 indicated as of thebridge-connected dry plate type, although other forms may be used. Thereturn circuit from the rectifier is completed by a connection back tothe secondary winding 5. The main windings 7b and 7c are similarlyprovided with half-wave electric valves 8b and Se, the circuit therefrompassing through a full wave rectifier a indicated as of thebridge-connected dry plate type, from which its return circuit passes tothe secondary winding 5a.

Each reactor is provided respectively with a biasing winding 10, 16a,10b and 100 supplied with direct current from any suitable sourceindicated as a battery 11. The windings 10 to 100 are connected inseries with each other and in series with an adjustable impedance device12. For Class A operation assumed in Fig. 1, the current in the windings10 to 10c is adjusted to have such relation to the current supplied bythe load windings as to bring the magnetization of the cores to a regionthat will result in the output current of the load windings being atabout the middle point of the steep portion of the output current curvewhen no current is supplied to the controlling windings later described.This condition corresponds to the point A of Fig. 7 with zero controlmagnetomotive force.

The control or controlling windings 13, 13a, 13b, and 130 are locatedrespectively on the reactor cores and are connected in series with eachother and supplied with current from the secondary winding 3a of thetransformer having the primary winding 3. The current in the primarywinding 3 is in one direction and varies in amplitude and in frequencyof pulsations when subjected to signals or audio input to themicrophone 1. The secondary winding 3a imparts current to thecontrolling windings 13 to 13c which is variable in amplitude and infrequency and also in positive and in negative directions as determinedby the signal input. With reference to the two upper reactor cores, thecontrolling windings should be connected in such relation to theirrespective main power windings and to each other that when themagnetomotive forces of the main and controlling windings'are in thesame direction in one reactor core, the same condition should apply tothe main and controlling windings on the other core under correspondingconditions. That is if a current which passes in the controlling circuitin one direction has its magnetomotive force in an aiding direction withthe magnetomotive force of the main winding in one core, then the samedirection of current in the controlling circuit should cause themagnetomotive force of the controlling winding to be in an aidingdirection with the magnetomotive force of the main winding on the othercore, as shown in Fig. 1. It follows that these controlling currentsimpose a variable controlling magnetomotive force on the reactorscorresponding to the control magnetomotive force of Fig. 7. Thisvariable controlling magnetomotive force affects the output current ofthe main windings and causes modulation of the output current from theload or main windings 7 and 7a so that the envelope of these currents isa function of the amplitude and wave form of the signal currents.

The foregoing likewise applies to the relationship of the controlwindings 13b and 13c to the windings 7b and 70. However, thesecontrolling windings 13b and 130 are connected in reversed relationrespectively with reference to the windings 13 and 13a, as shown in Fig.l, with the result that when the current in the controlling circuit ispassing in a direction to cause the output from the main windings 7 and7a to increase, the same direction of current will have the reverseeffect on the output of the main windings 7b and 7c and reduce theoutput current therefrom. When the current passes in the controllingcircuit in the opposite direction, the output from the windings 7b and7c is increased and the output from the windings 7 and 7a is decreased.This accomplishes the push-pull control of the amplifying reactors.

The biasing windings 10 to are subject to induced electromotive forcesby reason of being directly coupled with the other windings on thereactor cores; and in order to reduce the current due to the rippleinduced therein, the impedance device 12 in the circuit of the biasingwindings should have high resistance or inductance values, or else thebiasing windings themselves should have sufiiciently high resistance toproperly reduce the induced ripple currents. In some cases where thecores and value of the ampere turns of the main power windings 7 to 7care properly proportioned to deliver a current output corresponding tothe point A of Fig. 7 with zero control magnetomotive force, the biasingwindings may be omitted.

The currents derived from the main windings 7 and 7a of the upper set ofreactive means are demodulated by the rectifier 9 which delivers directcurrent from its output terminals as modulated by the audio signals; andsimilarly the output currents from the main windings 7b and 7c of thelower set of reactive means are demodulated by the rectifier 9a whichdelivers direct current from its output terminals as modulated by theaudio signals. The amplified signal output currents of the rectifiers 9and 9a are utilized to have a combined eifect upon the controlledcircuit in which may be connected any form of a transducer, such as theloud speaker 14. As shown in Fig. 1 two terminals of the rectifiers 9and 9a which have the same polarity are connected respectively to theend terminals of a primary winding 15 of a transformer, secondary 15a ofthe transformer serving to supply current to the loud speaker. Arnid-tap of: the primary winding 15 is connected to the other twoterminals of the rectifier-s having the same polarity. By reason of thisform of connection the current in one-half: of the primary winding isalways in the opposite direction to that in the other half. When nochange in the value of the current supplied to the primary winding 15occurs, as under the condition of no signal being imposed upon theamplifying apparatus, there is no electromotive force induced in thesecondary winding 15a owing to the counter-acting effect of the currentin the two halves of the primary winding 15. Now assume that anamplified signal wave has caused an increased current to be deliveredfrom the rectifier 9 to its half of the primary winding 15 and adecreased current to be delivered from the rectifier 9a to its half ofthe primary winding 15. As a result of the push-pull effect on the twopairs or sets of reactors as already explained, the resultant increaseof current in one-half of the winding 15 in one direction and theresultant decrease of current in the other half of the winding 15 in theopposite direction produces a cumulative effect upon the inducedelectromotive force in the secondary winding 15a with the result thatthe loud speaker or other transducer is pronouncedly affected by thecurrent supplied thereto. Similarly, when the amplifying signal wave inthe opposite direction results in a decrease in the output of thedemodulating rectifier-s 9 and 9a, the reverse effect takes place in thetwo halves of the primary winding 15 and an electrornotive force in theopposite direction is induced in the secondary winding 15a and therebycorrespondingly affects the loud speaker. Thus the variations in thefrequency and form arrests of the signal currents are greatly amplifiediii-the corresponding variations imposed upon the loud speaker or otherform of transducer.

In some cases, depending upon the characteristics of the loud speaker,an adjustable capacitor b may be connected in shunt across each half ofthe primary winding 15 for by-passing therefrom or filtering out, themain portion of the pulsations due to the high frequency car} rier wave.Also it is desirable in some cases to connect a low pass filter LPFacross the output circuit from the secondary winding 15a to reduce thepassage of currents to the loud speaker which would have no controllinginfluence thereon.

The coupling between the transducer and the output circuits of theamplifier may be modified fromthat shown in-Fig. 1. For example, Fig. 1aindicates a loud speaker 14a having built-in controlling windings fordirectly affecting the loud speaker output. These windings 16 and 16aare connected in series with each other with their outside terminalsconnected respectively to the terminals of the same polarity of thedemodulators 9 and 9a and a mid-connection connected directly to theother pair of terminals of the demodulators. Fig. 1b shows another formof coupling wherein an auto-transformer 17 has the terminals of itswinding connected respectively to terminals having the same polarity ofthe rectifiers 9 and'9a and a mid-tap connected to the other terminalshaving the same polarity. The circuit to the loud speaker 14 is shownconnected to equally distanttaps from the mid-connection of the winding17 through a capacitor 18. The capacitor 18 in the circuit to the loudspeaker serves to block the passage of direct current from the loudspeaker and permits only the varying currents to pass to the loudspeaker due to changes in values of the electromotive force imposed uponthe terminals of the loud speaker circuit. The modifications shown inFigs. 1a and 1b may be applied also to the other figures of thedrawings.

Fig. l, as already stated, shows for simplicity separate reactor coresand Fig. 8 shows an illustrative example of one form of a reactor corecombining two separate cores with their windings. The core 6k shown isof the three-legged type. The load windings 7 and 7a for example, are onthe outside legs of the core and their magnetomotive forces are in thesame direction in the outside legs, indicated by the arrows as from leftto right, and have a common direction in the middle leg. The controllingwindings 13 and 13a of Fig. l are combined ina single winding 13s on themiddle leg of the core in Fig. 8; and the biasing windings 10 and 10a ofFig. l are combined in a single winding 10s on the middle leg of thecore in Fig. 8. The mode of operation when using a reactor of the formof Fig. 8 is similar in a general way to that described with referenceto Fig. 1. It will be understood that in the other figures of thedrawings showing single forms of reactors they may be combined as shownin Fig. 8 or otherwise modified.

Fig. 2 is similar to Fig. 1 except the operation of the amplifyingreactors is under Class B as distinguished from Class A of Fig. l. inFig. 2 the secondary winding 3b of the transformer deriving current fromthe signal source is tapped at its mid-point and the lines from itsoutside terminals pass through one-way electric valves 19 and 19a.Current from the valve '19 passes through the controlling windings l3and 13a of the upper pairof reactorsand returns to the mid-tapconnection. Current from the valve 19a passes to the controllingwindings 13b and 130 of the lower pair of reactors and returns to themid-tap connection. in view of the currents in the control windingsbeing uni-directional, the reactor control is preferably Class B, andthe controlling windings are connected to cause their magnetomotiveforces to be additive to those of the main windings, asshown in Fig. 2.Also the currcnt in the biasing windings it) to 10c is preferablyadjusted to bring the output current of the load Windings {5 7 to 7c'atthe region B of Fig. 7 when no audio signals are imposed on theamplifying reactors. This gives a wide range of control from B to C ofFig. 7 with a corresponding increase in the amplification. Thecontrolling influence exerted on the lower pair of reactors is, as shownby the connections of the control windings, in the same direction asthat imposed upon the upper pair of reactors. It follows that when thesignal current eflect imposed on the secondary winding 3b is in onedirection, the upper pair of reactors may function over the range from Bto C in Fig. 7, while in the lower pair ofreactors the control currentis at a minimum or zero value. When the signal current effect imposed onthe winding 3b is in the opposite direction, the lower pair of reactorsfunction over a range from B to C of Fig. 7, while the control currentin the upper pair of reactors is at a minimum or zero value. In thiscase the control windings of the lower pair of reactors are connected tohave the same relationship to their main windings as regards directionof current, as the control windings of the upper pair of reactors haveto their main windings. In other respects, the operation of Fig. 2 issimilar to that of Fig. l, the current imposed on the halves of theprimary winding 15 controlling the output circuit being in oppositedirections toward its midtap.

Fig. 3 shows two stages of amplification wherein the first stage is asingle ended core set and the second stage is of the push-pull typehavingtwo core sets. An additional secondary winding 5b is shown in Fig.3 supplying current to the main windings 7d and 7e on a pair of cores 6dand 62. The currents from these windings pass through reversed connectedhalf-Wave valves 8d and 8e to a bridge-connected full wave rectifier 9 bfrom which a return connection is made to the secondary winding 5b. Thecontrol windings 13d and 13a are applied to these reactor cores andsupply a variable current in positive.

and negative directions derived from the secondary windiug 3a which isrelated to the signalsource. The biasing windings 10d and 10s arelikewise applied to the reactor cores and supplied with current from adirect current source 1141 through an impedance device 12a. Thedemodulated amplified signal current is supplied to the primary winding2t) of a transformer having a secondary winding 20a which in turnsupplies the control windings 13 to of the two pairs of amplifyingreactorssimilar to those disclosed in Fig. i. The output from thesereactors is supplied to the demodulating rectifiers 9 and 9a and to theloud speaker in the same manner as described with reference to Fig. 1.An adjustable capacitor 20b is preferably connected across the primarywinding 20 for by-passing therefrom the main portion of the pulsationsdue to the high frequency carrier wave. The first single ended stage ofamplification is preferably operated Class A and the second stage islikewise preferably operated Class A.

instead of the transformer 20, 20a and capacitor 20b for the couplingbetween the two stages, a modified form is shown in Fig. 3a wherein achoke 200 may be connected across the output of the rectifier 9b and acapacitor 26d connected in series in the circuit of the control windings13 to Be. The choke serves to bypass a major portion of unmodulateddirect current whereas the capacitor serves to transmit the amplifiedsignal currents to the com trol windings of the second stage.

Fig. 4 is similar to Fig. 3 except the alternating current output fromthe first stage is applied in proper phase relationship directly to thecontrol windings of the second stage through an impedance device 21inserted in the circuit of the control windings of the second stage.This results in the control windings 13 to 130 of the second stage beingsubjected to modulated currents with amplified audio current influences.The first stage should prefe'rably be operated Class A and likewise thesecond stage should be operated Class A. In placeof the impedance device21, a coupling transformer could-be used;

Fig. shows two stages of amplification wherein each of the stages is ofthe push-pull type. The second stage is similar to that shown in Fig. 1and is designated by corresponding reference characters. The first stageshows an upper pair of reactor cores 6f and 6g having main windings 7and 7g supplied from a secondary winding 50 and delivering currentthrough the reversely connected electric valves or half-wave rectifiers8f and 8g to a bridge-connected full wave rectifier 90 from which thecurrent returns to the secondary 5c. The lower pair of reactor cores 6hand 6i are provided with main windings 7/1 and 71' supplied with currentfrom the secondary winding 5d and deliver current through the reverselyconnected electric valves 811 and 81 to the bridge-connected full waverectifier 9d from which the current returns to the secondary winding 5d.The control windings 13 to 131i are respectively mounted on the cores 6fto 6i and supplied with current derived from the signal source. Thebiasing windings 10 to 10s are likewise applied to the cores andsupplied with current from a direct current source 11b through animpedance device 12b. The output of the demodulating rectifiers 9c and90? is supplied to a primary Winding 150 of a transformer, theconnections thereto being the same as described with reference toFig. 1. Its secondary winding d supplies current to the control windings13 to 13c of the second stage. The capacitors 15b and low pass filterLPF of each stage serve the same purpose as described with reference toFig. 1. Thus an amplified signal impulse is derived from the first stageof amplification and the secondary winding 15d delivers the amplifiedsignal current to the control windings 13 to 130 of the second stage ofamplification which in turn further amplifies the signal impulses. Theloud speaker 14, or other transducer, thus is subjected to a greatlyamplified series of impulses as result of this further amplification. Inview of the fact that the controlling current impulses impressed on bothstages of amplification is in both positive and negative directions,both stages would preferably be operated as Class A.

Fig. 6 is similar to Fig. 5 except instead of demodulating the signalimpulses delivered from the first stage of amplification, the outputfrom the two pairs of reactors of the first stage is deliveredrespectively to impedance devices 22 and 22a and then in proper phaserelation to the control windings 13 and 13a and to the control windings13b and 13c of the two pairs of reactors of the second stage. The twostages of Fig. 6 would preferably be operated as Class A. In place ofthe impedance de vices 22 and 22a, coupling transformers could be used.

In the foregoing disclosures the reactors have been of theself-saturating type but amplifiers with reactors which are notself-saturating may be used. Fig. 9 is a chart showing the generalrelationship between the output current from the main or load windingsof the latter type of reactor as the magnetomotive force of thecontrolling winding or windings is increased from zero to a value thatresults in maximum output. The figure shows the steep portion of thecurve from B to C. When this form of reactor is operated Class A, thebiasing of the core is made such that with zero control magnetomotiveforce corresponding to location A on the curve, the output current ofthe power winding will have a value corresponding to location A; andwhen operated Class B the biasing is made such that with zero controlmagnetomotive force corresponding to location B, the output of the powerwinding will have a value corresponding to location B on the curve. Inthe following disclosures using non-selfsaturating reactors separatecores are shown for simplicity but it will be understood they may becombined, one form of which is indicated in Fig. 8. When such a combinedtype of reactor is used as non-self-saturating, the load windings areconnected to cause their magnetomotive forces to act cumulatively witheach other in the outside legs of the core, as distinguished from thedirection of the arrows indicated on the outside legs in Fig. 8.

Referring to Fig. 10, the parts are similar to Fig. I exceptthat theload windings 7 to 70 have no one-way valves in series therewith. Thusin Fig. 10 the load windings are subjected to alternating current asdistinguished from intermittent direct currents. In Fig. 10 themodulated alternating currents of the load windings are delivered to thedemodulating rectifiers 9 and 9a respectively which in turn apply theamplified signal currents to the loud speaker or other transducerthrough the transformer connections already described with reference toFig. 1. In Fig. 10 the input to the controlling windings 13 to 13c fromthe signal source is variable not only in amplitude and frequency, butalso in direction. Thus the reactors of Fig. 10 should be operated ClassA; and in order to avoid objectionable distortion, the controllingmagnetomotive forces should not exceed in opposite directions the limitsof the locations B and C on the chart of Fig. 9. In this case theconnections of the control windings 13 to are made such that when thederived signal current passes in one direction, and the magnetomotiveforces of the control windings 13 and 13a are additive to themagnetomotive forces of the biasing windings 10 and 10a, themagnetomotive forces of the control windings 13b and 130 should then bein opposition to the magnetomotive forces of the biasing windings 10band 100, as shown in Fig. 10. When the derived signal current to thecontrol windings passes in the opposite direction, the reverse actiontakes place. This results in the condition that when the amplifiedsignal current is increased in one-half of the transformer primarywinding 15, it is simultaneously decreased in the other half giving theamplified push-pull effect.

Fig. 11 is similar to Fig. 2 except that the one-way valves are omittedfrom the circuits of the load windings 7 to 70. As distinguished fromFig. 10, the control windings of the non-self-saturating reactors aresubjected to currents in one direction only owing to the valves 19 and19:: being inserted in the circuits of the control windings. When signalimpulse currents pass to the control windings 13 and 13a of the upperpair of reactors, the control windings 13b and 130 of the lower pair ofreactors are inactive; and when the latter control windings are activethe control windings of the upper pair of reactors are inactive. Thisdisclosure would preferably be operated as Class B and the current inthe biasing windings 10 to 10c is adjusted to cause the output currentof the main windings to correspond to the location B when the controlwindings 13 to 130 have zero control magnetomotive force. The controlwindings of each pair of reactors are so connected with reference to themain windings to cause the output current from the main windings of eachpair to have a value within the range from B to C of Fig. 9 when thecontrol magnetomotive force is increased from zero value.

Fig. 12 is similar to Fig. 5 except in Fig. 12 the reactors of the firststage are non-self-saturating as described with reference to Fig. 10,whereas in the second stage of amplification the reactors are shown asof the self-saturating type. In this case both stages would be operatedas Class A.

The biasing windings on the reactor cores are indicated in the variousembodiments as being supplied by direct current from any suitableavailable source. Generally these windings would be connected in thecircuit to oppose the magnetomotive force of the main windings forsecuring the biasing for operation as Class A or Class B and in somecases these windings may be connected to create a magnetomotive force inthe opposite direction, thus acting with that of the main windings forobtaining the desired results. In some cases these windings may beomitted when the magnetomotive forces of the main load windings areadjusted to create the condition for Class A or Class B operation asdesired in the particular instance.

- In general as to all of these disclosures the best results areobtained by the use of material in the reactor cores which has thehighest constant permeability up to the saturation point, unitypermeability beyond saturation, the smallest area of the hystersis loopand the lowest eddy current losses.

As regards the source of the power supply and the obtaining of thedesired frequency of this source, it will be understood that any of theavailable types may be used such as rotating machines of high frequency,oscillatory tubes and other forms.

In the foregoing disclosures the input audio signal to the controllingwinding or windings of the initial stage of amplification has beenindicated as derived from a carbon microphone. However, the signalsource may be of any character and may be variously coupled to thecircuit of the controlling winding or windings. Also the signal inputmay be derived from other types of microphones, phonograph pick-ups,radio receiver detector outputs and so forth.

In some cases instead of using a pair of individual reactor cores asshown herein, or a combined core as shown in Fig. 8, only one core witha power winding, a controlling winding and a biasing winding thereon maybe used with some provision such as a low pass filter in the circuit ofthe controlling winding for avoiding induced electromotive forces in thecontrolling winding.

It will be understood that this invention may be moditied in variousways as to the form of the reactors, the coupling to the signal source,the character of the signal source, the coupling to the loud speaker oroutput circuit, the number of amplifying stages and the character of thestages and the coupling between amplifying stages. Also various forms offilters may be used and connected in a manner to improve the quality andvolume of the amplified output. Also the invention may be utilized invarious applications for amplification of signals or controls within theaudio range without departing from the scope thereof.

I claim:

1. A magnetic amplifier for amplifying audio signals from a signalsource, said amplifier comprising an input circuit for receiving analternating current having a frequency higher than the highest audiofrequency to be amplified, two pairs of branches connected to beenergized from said input circuit, each branch having a one-way valveand saturable reactor means including a main winding and control windingmeans for receiving audio signals from said signal source to modulatethe currents of the main winding, each branch having a series circuitincluding the main winding and the one-way valve of the branch, saidseries circuits of each pair of branches being connected in parallel andone end of each pair of branches being connected to said input circuit,each pair of branches having connected to its other end an outputcircuit with a return path of said input circuit and the valves in eachpair of branches being oppositely poled to deliver alternating currentto each of said output circuits, said control winding means beingrelated to said main windings to have reversed effects on the respectivepairs of branches, a demodulator in each of said output circuits fordemodulating the alternating currents in said output circuits, and anaudio output transformer having input winding means with symmetricalhalves, one of said halves being connected to receive the output of oneof said demoduiators, the other of said halves being connected toreceive the output of the other demodulator, said halves being relatedto provide a cumulative audio frequency effect in response tosimultaneously rising output currents of one demodulator and fallingoutput currents of the other demodulator.

2. A magnetic amplifier for amplifying audio signals from an audiofrequency signal source, said amplifier comprising an input circuitreceiving an alternating current having a frequency higher than thehighest audio frequency to be amplified, two pairs of branches connectedto be energized from said input circuit, each branch including a one-wayvalve and saturabie reactor means having a main winding and a controlwinding, each branch having a series circuit including the main windingand the one-way valve of the branch, said series circuits of each pairof branches being connected in parallel and one end of each pair ofbranches being connected to said input circuit, each pair of brancheshaving connected to its other end an output circuit with a return pathto said input circuit and the valves in each pair of branches beingoppositely poled to deliver alternating current to each of said outputcircuits, said control windings being interconnected to receive audiosignals from the signal source for modulating the currents in the mainwindings, said control windings being related to said main windings tohave reversed effects on the respective pairs of branches, a pair offullwave bridge rectifiers, one in each of said output circuits fordemodulating the alternating currents in said output circuits, and anaudio output circuit for converting audio frequency currents into soundWaves of the same frequency as said audio frequency signals, said audioouput circuit having an input winding with opposite end terminals and anintermediate terminal, one of said end terminals being connected to anoutput terminal of one polarity of one of said rectifiers, the other ofsaid end terminals being connected to the output terminal of said onepolarity of the other rectifier, said intermediate terminal beingconnected to the output terminals of the other polarity of bothrectifiers.

3. A magnetic amplifier for amplifying audio signals from a signalsource, said amplifier comprising an input circuit for receiving analternating current having a frequency higher than the highest audiofrequency to be amplified, two pairs of branches connected to beenergized from said input circuit, each branch including a one-way valveand saturable reactor means having a main winding and control windingmeans, each branch having a series circuit including the main windingand the one-way valve of the branch, said series circuits of each pairof branches being connected in parallel and one end of each pair ofbranches being connected to said input circuit, each pair of brancheshaving connected to its other end an output circuit with a return pathto said input circuit and the valves in each pair of branches beingoppositely poled to deliver alternating current to each of said outputcircuits, said control winding means being interconnected to receiveaudio signals from the signal source for modulating the currents of themain windings, said control winding means being related to said mainwindings to have reversed effects on the respective pairs of reactorbranches, a pair of full-wave bridge rectifiers, one in each of saidoutput circuits for demodulating the alternating currents in said outputcircuits, and an audio output section for converting audio currents intoaudible reproductions of said audio signals, said section comprisingelectromagnetic winding means with symmetrical halves, one of saidhalves being connected to receive the output of one of said rectifiers,the other of said halves being connected to receive the output of theother of said rectifiers, said halves being related to provide acumulative audio effect in response to simultaneously rising outputcurrents of one rectifier and falling output currents of the otherrectifier.

References Cited in the file of this patent UNITED STATES PATENTS1,847,079 Burton Mar. 1, 1932 2,027,311 Fitz Gerald Ian. 7, 19362,108,642 Boardman Feb. 15, 1938 2,164,383 Burton July 4, 1939 2,306,998Claesson Dec. 29, 1942 2,338,423 Geyger Jan. 4, 1944 2,504,675 ForssellApr. 18, 1950 2,509,738 Lord May 30, 1950 2,509,864 Hedstrom May 30,1950

